Introduction: The advent of next generation sequencing has hugely enhanced our ability to sequence DNA but has also created a new clinical challenge in the variant of unknown significance (VUS). A VUS is a rare change in DNA sequence that based on our current knowledge cannot be classified as pathogenic or benign. The VUS challenge is very prominent in the case of the cardiac ryanodine receptor gene (RyR2). Mutations of RyR2 can cause life-threatening arrhythmias which can lead to sudden cardiac death in young and apparently healthy individuals. Induced pluripotent stem cell derived-cardiomyocytes (iPSC-CMs) from patients carrying the VUS in addition to iPSC-CMs where the VUS has been corrected using CRISPR technology could be used as a novel approach to determine pathogenicity of a VUS. Objective: In this work we tested various CRISPR-based strategies to either correct a RyR2 VUS or suppress the expression of the VUS allele in iPSC-CMs. The iPSC-CMs were generated from a patient who suffered a cardiac arrest and carries a nonsense change of the RyR2 gene (R4790*). Methods and Results: Initially we attempted direct genome editing of the VUS using an endonuclease cut followed by homology directed repair. We used two CRISPR-Cas enzymes: Cas9 and Cas12a. This approach failed because of low cutting efficiency at the site of the mutation. We then tried to induce a premature stop codon on the VUS allele via a CRISPR-Cas9 mediated DNA cut followed by non-homologous end joining DNA repair. This approach induced an early stop codon as demonstrated by next generation sequencing (5 different clones analysed). An early stop codon is expected to decrease the levels of mRNA by causing nonsense mediated decay; however, this did not occur in our experiments. The expression levels of mRNA carrying the early stop codon and the VUS did not decline as shown by qPCR (n=3 per each clone). Finally, we attempted to reduce VUS allele expression by induction of a large deletion in the RyR2 VUS allele. Suppression was obtained by inducing a big gene deletion which includes two different gRNAs and insertion of puromycin resistance cassette by homologous directed DNA repair. RyR2 gene deletion was confirmed by Sanger sequencing of both genomic and coding DNA (12 clones analysed). Conclusions: This study shows that CRISPR technology can edit the RyR2 gene; however, the success of the gene editing is dependent on the DNA region targeted. Moreover, allele suppression in the RyR2 gene can be only achieved by a big deletion of the gene. As recent evidences on mouse models of RyR2-derived arrhythmias demonstrated that silencing of RyR2 mutant mRNA reduces arrhythmia episodes, our approach may develop a novel therapeutic strategy for RyR2-derived arrhythmias.